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921.
C. Warneke R. Holzinger A. Hansel A. Jordan W. Lindinger U. Pöschl J. Williams P. Hoor H. Fischer P. J. Crutzen H. A. Scheeren J. Lelieveld 《Journal of Atmospheric Chemistry》2001,38(2):167-185
Airborne measurements of volatile organic compounds (VOC) were performed overthe tropical rainforest in Surinam (0–12 km altitude,2°–7° N, 54°–58° W) using the proton transferreaction mass spectrometry (PTR-MS) technique, which allows online monitoringof compounds like isoprene, its oxidation products methyl vinyl ketone,methacrolein, tentatively identified hydroxy-isoprene-hydroperoxides, andseveral other organic compounds. Isoprene volume mixing ratios (VMR) variedfrom below the detection limit at the highest altitudes to about 7 nmol/molin the planetary boundary layer shortly before sunset. Correlations betweenisoprene and its product compounds were made for different times of day andaltitudes, with the isoprene-hydroperoxides showing the highest correlation.Model calculated mixing ratios of the isoprene oxidation products using adetailed hydrocarbon oxidation mechanism, as well as the intercomparisonmeasurement with air samples collected during the flights in canisters andlater analysed with a GC-FID, showed good agreement with the PTR-MSmeasurements, in particular at the higher mixing ratios.Low OH concentrations in the range of 1–3 × 105molecules cm-3 averaged over 24 hours were calculated due to lossof OH and HO2 in the isoprene oxidation chain, thereby stronglyenhancing the lifetime of gases in the forest boundary layer. 相似文献
922.
Ekaterine Batchvarova Svan-Erik Gryning Charlotte Bay Hasager 《Boundary-Layer Meteorology》2001,99(3):489-507
Based on measurements at Sodankylä Meteorological Observatory the regional (aggregated) momentum and sensible heat fluxes are estimated for two days over a site in Finnish Lapland during late winter. The forest covers 49% of the area. The study shows that the forest dominates and controls the regional fluxes of momentum and sensible heat in different ways. The regional momentum flux is found to be 10–20% smaller than the measured momentum flux over the forest, and the regional sensible heat flux is estimated to be 30–50% of the values measured over a coniferous forest.The regional momentum flux is determined in two ways, both based on blending height theory. One is a parameterised method, the other represents a numerical solution of an aggregation model. The regional sensible heat flux is determined from the theory of mixed-layer growth. At near neutral conditions the regional momentum flux can be determined independently of the regional sensible heat flux. At unstable conditions the two models become coupled.The information that is needed by the parameterised blending height method and by the mixed-layer evolution method in order to derive the regional fluxes of momentum and sensible heat can be obtained from radiosonde profiles of wind speed and temperature. 相似文献
923.
Temporal Surface Ozone Patterns in Urban Manitoba, Canada 总被引:1,自引:0,他引:1
This study examined temporal surface ozone patternsfor two urban centres in Manitoba,Canada by analyzing hourly concentrations at theWinnipeg downtown (1995–1999), Winnipegresidential (1995–1999) and Brandon industrial(1998–1999) monitoring sites. The characteristicannual ozone cycle and diurnalcycles for June and December were attributable to: (1) theannual and diurnal solar radiation cycles,(2) temporal variations in the emissions of precursorchemical compounds, in particular the source strength ofnitrogen oxides, (3) temporal variationsin the height of the mixed layer, which determinethe degree of dilution of these emissions byatmospheric dispersion, and (4) an in situvolatile organic compound sensitive photochemicalregime, which resulted in decreased concentrations ofozone in response to increasedconcentrations of nitrogen oxides. Onlyone exceedance of the maximum acceptable level of82 ppb was recorded in the study period; itoccurred at the Brandon monitoring site on June 6, 1999.The sequence of weather and the hourly concentrationsof ozone and nitrogen oxides indicatedthat: (1) ozone fumigation, with the transition fromthe nocturnal boundary layer to the daytime mixed layer, mayhave supplemented photochemical ozone formation duringthe morning hours, and (2) during theevening hours, the post cold-frontal downward flux ofozone rich air, which was in the region dueto atmospheric transport, stratosphere-troposphere-exchangeor, possibly, due to the multiplicityof thunderstorms in the area in lateafternoon – early evening, may have been the main cause ofthis rare exceedance event. 相似文献
924.
Ulrich C. E. ZANKE Prof Institute of Hydraulic Engineering University of Technology Darmstadt Germany 《国际泥沙研究》2001,16(1)
l PROBLEMS AND AlMSSediments may be transported close to the bed, rolling and sliding, as we1l as susPended in the flow. Forvarious reasons the theoretical treatment of the bed-load problem has been exceptionally difficult. Noanalytical solution had been fOund uP to now, beginning with Du Buat (l786), Huebbe (l86l) and DuBoys (I 879). Since the aPProach of Du Boys numerous new attemPts have been catried out, mostly of anempirical nature. Consequently they are not generally valid an… 相似文献
925.
MODELING OF THE HIGH CONCENTRATION LAYER OF COHESIVE SEDIMENT UNDER THE ACTION OF WAVES AND CURRENTS
Qinghe ZHANG Yongsheng WU Jijian LIANand Pingxing DING School of Civil Engineering Tianjin University Tianjin China Dept. Hydraulic Engineering Tsinghua University Beijing China State Key Lab. of Estuarine Co 《国际泥沙研究》2001,16(2)
MODELING OF THE HIGH CONCENTRATION LAYEROF COIIESIVE SEDMNT UNDER Tus ACTIONOF WAVES AND CURRENTSQinghe ZHANG', Yongsheng WU', Jiian LIAN1 and Pingxing DING3Abstract:High concenhation layer of cohesive sediment frequenhy occurs in muddy estUaries and coastalzones, and causes raPid siltation of the waterways. A one dimensional vertical coupled modeldescribing the interactions betWeen waves, currentS and suspended cohesive sediment is develoPed inthe pre… 相似文献
926.
927.
Liu Shuhu Liu Heping Liang Fuming Wu Fenglei M. Y. Lecler Xu Mei Hong Zhongxiang Li Jun Liu Huizhi Na Jingyang 《Acta Meteorologica Sinica》1997,11(3):328-337
Described in this paper is an experiment on atmosphere-surface turbulent exchange and boundary layer turbulence properties conducted in July 1994 over the Kerqin Grassland,Jilin,China.The characteristics of the turbulent spectrum,and the relationships of the standard deviation of the turbulent velocity components and sensible heat flux with the atmospheric stability are studied using data from a sonic anemometer and a fast-response platinum resistance thermometer mounted on a 100 m tower.The results show that in the surface layer over a flat,uniform and open grassland,for a broad stability range(-22.12≤ZiL≤17.98),the velocity spectra obey the-2/3 power law in the inertial subrange,and 1 power law at low frequencies.Under near neutral stratification,σu/u*=1.20,σv/u*=1.23 and σw/u*=1.02.For Zi/L≤-0.2,the standard deviations of the turbulent velocity components follow a 1/3 power law.For Zi/L≤-0.1,the standard deviation of the temperature fluctuations follows a-1/3 power law,and as Zi/L≤-0.08,it exhibits nonlinear behavior.Sensible heat flux is well correlated to the stability parameter. 相似文献
928.
本文设计了一冠层(CL)和大气边界层(ABL)之间物质和动量交换的耦合模式,并对CL内风速、物质随高度分布和日变化作了数值模拟.结果表明,由大尺度扩散引起冠层低层的第二个风速极大和多极值的浓度分布,CL内湍流通量和物质浓度随高度减小而迅速降低,以及CL动量减小对浓度分布的重要影响,模式都能很好地描述,模拟结果与观测事实有好的一致性.利用浓度和温度廓线相似假设,导出了质量汇的经验关系. 相似文献
929.
Based on the HEIFE 1988 and 1990 pilot observations,an analysis on the turbulence structure of Gobi surfacelayer,mainly on the similarity formulations of wind and temperature variances,the spectra and cospectracharacteristics,is presented.The phenomenon of downward water vapor flux over Gobi desert in daytime is confirmedin both observations,this and the well-known‘oasis effect’are two sides of a local mesoscale circulation. 相似文献
930.
G. W. Harris D. Klemp T. Zenker J. P. Burrows B. Mathieu 《Journal of Atmospheric Chemistry》1992,15(3-4):315-326
Measurements of NO2, HCHO, and H2O2 were made by the highly specific method of mid infra-red absorption spectroscopy using tunable diode lasers (TDLAS) during the 1988 Polarstern expedition. The TDLAS data are compared to those obtained during the cruise using less direct methods. Southern Hemisphere NO2 levels suggest nett photochemical destruction of O3 in the boundary layer. Northern Hemisphere HCHO averaged 0.47±0.2 ppbv; the HCHO measurements are used in a simple calculation to estimate OH noontime maxima of 3–6×106 cm-3. 相似文献